Presently, when air bag covers are provided in automobiles on the driver side of the vehicle, the air bag is stored in the steering column behind an air bag cover. During automatic inflation of the air bag, the air bag cover moves away from the steering column to permit its safety function between the steering column and the operator of the vehicle. Air bag covers may also be provided on the passenger side of the vehicle as well.
Recent practice in the automotive industry is utilization of all plastic fabricated air bag covers. Conventional air bag covers used in conjunction with occupant restraint systems often include noticeable or visually perceptible tear seams or scores disposed on the exterior surface of the air bag cover. The tear seams or scores represent selected weakened surfaces where the inflating air bag initially separates or breaks through the air bag cover and moves away from the steering wheel to perform its safety feature.
U.S. Pat. No. 4,325,568 issued to Clark et al. discloses a modular occupant restraint system including an inflator, a cushion, a container for the cushion and an air bag cover for the container assembled as a module. Clark et al. further discloses the use of score lines that are visually perceptible from a front view of the air bag cover as it is operably mounted on the steering wheel of the automobile.
U.S. Pat. No. 5,085,462 issued to Gaultier discloses an air bag and vehicle horn switch assembly. The assembly of Gaultier also discloses use of an air bag cover including visually perceptible exterior break seams or score lines in the operable mounted position within the vehicle.
U.S. Pat. No. 5,186,490 issued to Adams et al. discloses a cover for an inflatable restraint system for a motor vehicle which contains a slot in the upper wall thereof into which a thin or membrane type switch assembly is inserted. Adams et al. further discloses an air bag cover having an injection molded thermoplastic upper wall and a soft outer cover exposed to the interior of the vehicle manufactured from urethane, vinyl or polyester. The outer cover completely encompasses and overlaps the upper wall structure and uninflated air bag forming two structures the air bag must exit to carry out its function.
It is also known that the provision of noticeable exterior break seams or score lines that are designed for aesthetic purposes is very difficult to achieve as the final design obtained must satisfy engineering requirements related to inflation and exit of the air bag. Thus, use of visually noticeable exterior outer score lines is limited to known score line designs such as the "H" shaped score lines disclosed in U.S. Pat. No. 5,085,462 to Gaultier.
There has been attempts to hide the break seam on the air bag cover, as illustrated in U.S. Pat. No. 5,498,026 and the above-noted application.
One problem with such a hidden break seam is that the occupant of the vehicle does not know whether an air bag device is in the vehicle and, consequently, such hidden break seams may cause some anxiety.
Typically, a tear seam is formed into an air bag cover by injecting plastic into an injection mold in which the mold cavity includes a projection defining the tear seam. An example is illustrated in U.S. Pat. No. 5,335,935 issued to Proos et al. However, with this method it is difficult to inject the plastic over the projection, resulting in swirl lines caused by turbulence. Also, it is very difficult to have molten plastic flow over the projection, therefore, the thickness of the tear seam is limited, typically 0.4 millimeters or more.
U.S. Pat. No. 5,320,380, issued to Hamada et al., discloses an air bag cover having a hidden tear seam of less than 0.4 millimeters. However, this air bag cover is manufactured utilizing RIM (Reaction Injection Molding) technology. With RIM, a mold cavity supporting a mesh screen is injected with two liquid materials that chemically react to form a thermoset product. However, a product manufactured utilizing RIM molding is relatively more expensive, less durable and heavier than a product manufactured utilizing thermoplastic injection molding.
U.S. Pat. Nos. 5,549,324; 5,536,037; and 5,312,130 disclose physical air bag doors on vehicle instrument panels.
U.S. Pat. Nos. 5,664,801; 5,662,350; and 5,588,669 disclose covers for air bag modules having visible seams.
U.S. Pat. No. 5,447,328 discloses an instrument panel having an integral door cover for concealing an air bag that is cast in a special mold with a raised apex rib that forms grooves outlining a flap.
U.S. Pat. No. 5,382,398 discloses a method for fabricating an interior furnishing part in which a material sheet is provided with a recess or rib in the exterior face during molding.
U.S. Pat. No. 5,571,597 discloses a molded trip panel that is circumscribed by a simulated seam.
U.S. Pat. No. 5,558,364 discloses a plastic air bag cover having an integrated light source for use in a passenger compartment which is transmitted through indicia stating "SRS Airbag".
U.S. Pat. No. 5,683,101 discloses an automotive seat plastic air bag cover having transparent indicia noting "SRS".
U.S. Pat. No. 5,639,116 discloses a physical opening allowing access to an air bag module for maintenance.
U.S. Pat. No. 5,650,115 discloses a method of making air bag covers by enclosing the cover material in a mold, and advancing a projection on a mold portion against a covering material to form a tear seam.
U.S. Pat. No. 5,567,375 discloses a method and apparatus for forming an air bag cover with a lesser strength tear strip insert.